Highland Boundary Fault

It separates two different geological terranes which give rise to two distinct physiographic terrains: the Highlands and the Lowlands, and in most places it is recognisable as a change in topography.

Aligned southwest to northeast from Lochranza on Arran, the Highland Boundary Fault bisects Bute and crosses the southeastern parts of the Cowal and Rosneath peninsulas, as it passes up the Firth of Clyde.

[8] On discovering this, Hall and Dagley concluded that the observed trend, which followed the length of the Dalradian trough, transition from positive to negative anomalies.

[3] The fault allowed the Midland Valley to descend as a major rift by up to 4,000 m (13,000 ft) and there was subsequent vertical movement.

[12] The Dalradian Supergroup consists of metasedimentary rocks which underwent polyphase deformation and metamorphism during the Precambrian and early Paleozoic.

The Dalradian metasedimentary rocks are overlain by an obducted ophiolite that is continuous for at least several kilometres on either side of the Highland Boundary Fault.

[3][13][14] Evidence for the Acadian displacement event is based on the geochemical study of detrital garnets in the Lower Old Red Sandstone on the Northern limb of the Strathmore Basin.

These garnets were linked to those in isolated Dalradian sediments in the northwest, providing evidence for post-Early Devonian (Acadian) movement to be only few tens of kilometers.

[13][14] In addition, the Lintrathen ignimbrite, which is present at the base of the Lower Devonian sequence was traced along the fault and it was found that the displacement was both short and lateral.